Federal Communications Commission (FCC) rulings have opened up the possibility of wireless network deployments over vacant UHF (ultra-high frequency) and VHF (very high frequency) television (TV) channels, also commonly known as “white spaces”. A key requirement for any white space device under this ruling is that its transmissions do not interfere with incumbents, namely TV transmitters and licensed wireless microphones. The ruling stipulates that devices must learn about occupied TV channels and registered wireless microphones either by sensing or by accessing a geolocation database (e.g., on the Internet).
A concern about the use of white spaces is utilization. This is to a large extent due to the requirement that white space devices must “vacate an entire TV channel”, even if there is only a single wireless microphone operating in this TV channel. Given that a TV channel is 6 MHz wide (in the US) or 8 MHz wide (in most other countries), and a microphone occupies only a few 100 KHz, this is a waste of available white spaces.
In urban scenarios and on a campus where there can be several microphones in operation at any given time, the requirement to vacate an entire TV channel whenever there is a microphone operating in this channel can imply that a large fraction of the available white space spectrum is wasted. In extreme cases, it can even lead to scenarios where there is no usable white space spectrum available at all, even though the amount of actually utilized spectrum (by the microphones) would be a tiny fraction of the spectrum.